FileTest

FileTest implements file test operations similar to those used
in File::Stat. It exists as a standalone module, and its
methods are also insinuated into the File class. (Note that
this is not done by inclusion: the interpreter cheats).

If file_name is readable by others, returns an integer
representing the file permission bits of file_name. Returns
nil otherwise. The meaning of the bits is platform dependent;
on Unix systems, see stat(2).

If file_name is writable by others, returns an integer
representing the file permission bits of file_name. Returns
nil otherwise. The meaning of the bits is platform dependent;
on Unix systems, see stat(2).